Method of making isopropyl esters of aliphatic acids



Patented Dec. 10, 1940 UNlTED STATES PATENT OFFICE METHOD OF MAKINGISOPR-OPYL ESTERS F ALIPHATIO ACIDS Gerald B. Coleman, Midland, Micln,assignor to The Dow Chemical Company, Midland, Mich.,

a corporation of Michigan No Drawing. Application October 21, 1935,Serial No. 45,984

8 Claims. (c1. 260-497) to polymerization, charring, etc., of thepropylene by the sulphuric acid.

In British Patent 334,228 a methodis described whereby propylene isreacted with a solution comprising equal volumes of acetic and sulphuricacids at temperatures below 60 C., the reacted mixture is diluted withwater, the organic and aqueous layers of the resultant mixture areseparated, and each layer is distilled. Isopropyl acetate and isopropylalcohol are collected as distillates from the respective layers.

Suida, in U. S. Patent No.1,836,135,has described a method wherebypropylene is reacted with a dilute aqueous aliphatic acid in thepresence of a relatively small quantity of a catalyst, i. e. sulphuricacid, naphthalene-sulphonic acid, benzene-sulphonic acid, etc., thereaction mixture being heated under pressure at a temperature above 100C. By operating in such manner, polymerization and charring of organicreactants are said to be largely avoided, but a mixture of isopropylalcohol and an isopropyl ester is always formed. 0 Brezinski, in U. S.Patent No. 1,951,747, discloses the preparation of an ester of analiphatic acid by heating an olefine, e. g. propylene, with a carboxylicacid, e. g. acetic acid, under pressure in the presence of a non-acidiccatalyst such as zinc chloride, ferric chloride, potassium sulphate,charcoal, etc. The yield of ester product by such method is apparentlylow, the highest yield reported in the examples of the patent being only12.5 per cent of theoretical.

In a co-pending application, Serial No. 597,- 803, filed May 9, 1932which has matured into Patent No. 2,021,851, of which the presentapplication is a continuation-in-part, I, have disclosed that inpreparing an isoprop l ester of an aliphatic acid from propylene andsuch acid, the difficulties mentioned above may be avoided and the esterbe produced in good yield and as substantially the only reaction productby carrying the reaction out under pressure in the presence of an acidiccompound as catalyst, and have claimed the aforesaid method usingsulphuric acid as the catalyst.- The present application dealsparticularly with the use of certain acidic sulphuric acid derivativesas catalysts for the reaction. By an acidic sulphuric acid derivative" Imean a derivative of sulphuric acid, containing no metal ions, which isacid in reaction or may be hydrolyzed by water to produce an acidsolution. Methyl sulphuric acid, dimethyl sulphate, ethyl sulphuricacid, diethyl sulphate, isopropyl sulphuric acid, chloro-sulphonic acid,ethyl chloro-sulphonate, benzene-sulphonic acid, methyl or ethylbenzene-sulphonate, and naphthalene di-sulphonic acid are illustrativeof the class of catalysts herein referred to.

In preparing an isopropyl ester of an aliphatic acid by the presentmethod, a mixture of propylene, a substantially anhydrous aliphaticacid, e. g.

acetic acid, etc., and an acidic sulphuric acid derivative, e. g.diethyl sulphate, benzene-sulphonic acid, etc., is heated under pressureto a temperature above C., but below that at which the reactioncomponents are decomposed,

preferably between 100 and 250 C. The propylene is preferably employedin a proportion at least chemically equivalent to the aliphatic acid,but may be employed in smaller proportion, if desired. The acidicsulphuric acid derivative is employed in a catalytic proportion, i. e.in a proportion less than that chemically equivalent to the propylene.In practice I prefer to employ less than .05 mol of catalyst per mol oipropylene used. The reaction usually is substantially complete afterfrom 4 to 8 hours of heating, but longer heating may in some instancesbe required. Following the reaction, the ester product may be separatedin substantially pure form by direct distillation from the reactedmixture.

The following examples describe several ways in which the principle ofthe invention has been applied, but are not to be construed as limitingthe invention:

' Example I Into an iron bomb of the rotating type were placed 120 grams(2.0 mol's) of glacial acetic acid and 23.3 grams (0.2 mol) ofchloro-sulphonic acid. Approximately 94.5 grams (2.25 mols) offractionally distilled, 120.4 grams (1.18 mols) of substantially pureisopropyl acetate being separated. The yield of isopropyl acetate was 59per cent of theoretical, based on the quantity of acetic acid employed.No isopropyl alcohol was obtained.

Example II 120 grams (2.0 mols) of glacial acetic acid, 94.5

grams (2.25 mols) of propylene, and 12.6 grams (0.1 mol) of dimethylsulphate were reacted as in Example I. The bomb was cooled, the chargeremoved therefrom, and fractionally distilled to give 158 grams (1.55mols) of substantially pure isopropyl acetate, the yield being 77.4 percent of theoretical based on the quantity of acetic acid used. Noisopropyl alcohol was obtained.

Example III Example IV A mixture of 148 grams (2.0 mols) ofsubstantially anhydrous propionic acid, 96.6 grams (2.3 mols) ofpropylene, and 15.4 grams (0.1 mol) of diethyl sulphate was heated in arotating bomb at approximately 150 .C. for 5 hours. The bomb was thencooled, the charge removed therefrom, and 145.5 grams (1.25 mols) ofsubstantially pure isopropyl propicnate separated by fractionaldistillation of the reacted mixture. The ester product was obtained in62.7 per cent of the theoretical yield based on the quantity ofpropionic acid used. 30.7 per cent of the propionic acid was recoveredduring distillation. No isopropyl alcohol was obtained.

Similarly, other aliphatic acids, such as butyric, valeric, isovaleric,etc., may be reacted with propylene under the conditions hereinbeforedescribed to produce the corresponding esters in good yield.

Although the examples given were carried out in batch manner by heatingthe reaction mixture under its vapor pressure in a bomb, during plantoperation the reactants may be continuously pumped into a reactor of atype suitable for continuous operation, e. g. a tubular reactor. Thepressure may advantageously be suflicient to maintain all components ofthe reaction mass in liquid form during reaction, in which case amechanical pressure greater than the vapor pressure of the reactionmixture is applied. The reacted mixture may be withdrawn continuouslyfrom the reactor and fractionally distilled to separate the pure esterproduct. The unreacted components of the mixture, e. g. propylene,aliphatic acid, and the catalyst, may be returned to the reactor alongwith fresh quantities of propylene and the desired aliphatic acid. Afteroperating in such manner through several cycles, an equilibrium would bereached, so that thereafter the quantities of propylene and aliphaticacid added in a given cycle are converted directly into the desiredester product in the same cycle.

In the examples substantially Pure propylene was employed as a reactant.Impure propylene, e. g. propylene containing an appreciable quantity ofimpurities such as saturated hydrocarbons, ethylene, etc., may, however,be employed successiully as a reactant for the preparation of isopropylesters according to the present method. If the propylene contains anappreciable quantity of the more reactive higher oleflnes, such asbutylenes, amylenes, etc., a mixture of esters will, of course, beformed. Ethylene, on the contrary, maybe present in a considerableproportion without reacting to form undesirable by-products.

In each of the foregoing examples, the ester product was separated fromthe reacted mixture through fractional distillation of the latter. Anytendency of the reacted mixture toward charring may be avoided bycarrying the last stage of the fractional distillation out undersub-atmospheric pressure. Instead of separating the ester product fromthe reaction mixture through direct distillation of the latter,the'cooled reaction mixture may,'of course, be neutralized with a basicmaterial, washed with water, dried, and finally purified throughdistillation. However, such intermediate steps ordinarily areunnecessary in practicing the invention.

The present invention, in brief, comprises reacting propylene with asubstantially anhydrous aliphatic acid in the presence of a catalytic.

C., under superatmospheric pressure to form any isopropyl ester of saidaliphatic acid as substantially the only reaction product, andthereafter separating the isopropyl ester from the reacted mixture.

Other modes of applying the principle of my invention may be employedinstead of those explained, change being made as regards the methodherein disclosed, provided the step or steps stated by any of thefollowing claims or the equivalent of such stated step or steps beemployed.

I therefore particularly point out and distinctly claim as my invention:

1. In a method of making an isopropyl ester of an aliphatic acid, thestep which consists of reacting propylene with a substantially anhydrousaliphatic acid under super-atmospheric pressure and in the presence of acatalyst consisting of not more than 0.05 mol for each mol of propylenepresent in the reaction mixture of an acidic sulphuric acid derivativeselected from the group consisting of the aryl sulphonic and chlorosulphonic acids and the lower alkyl esters of sulphuric, aryl sulphonicand chloro sulphonic acids.

2. In a method of making isopropyl esters of an aliphatic acid, the stepwhich consists of reacting propylene with a substantially anhydrousaliphatic acid under super-atmospheric pressure at a temperature betweenabout 75 C. andabout 250 C. and in the presence of a catalyst consistingof not more than 0.05 mol for each mol of propylene present in thereaction mixture of an acidic sulphuric acid derivative selected fromthe group consisting of aryl sulphonic and chloro sulphonic acids andlower alkyl esters of sulphuric, aryl sulphonic and chloro sulphonicacids.

3. In a method of making isopropyl acetate, the stepwhich consists inreacting propylene with substantially anhydrous acetic acid undersuperatmospheric pressure and in the presence of a catalyst consistingof not more than 0.05 mol for each mol of propylene present in thereacting mixture of an acidic sulphuric acid derivative selected fromthe group consisting of the aryl sulphonic and chloro sulphonic acidsand lower alkyl esters of sulphuric, aryl sulphonic and chloro sulphonicacids.

4. In a method of making isopropyl acetate, the step which consists inreacting propylene with substantially anhydrous acetic acid undersuperatmospheric pressure at a temperature between about 75 C. and about250 C. and in the presence of a catalyst consisting of not more than0.05 mol for each mol of propylene present in the reaction mixture of anacidic sulphuric acid derivative selected from the group consisting ofthe aryl sulphonic. and chloro sulphonic acids and lower alkyl esters ofsulphmic, aryl sulphonic and chloro sulphonic acids.

5. In a method of making an isopropyl ester of an aliphatic acid, thesteps which consist of reacting propylene with a substantially anhydrousaliphatic acid under super-atmospheric pressure and in the presence or acatalyst consisting of not more than 0.05 mol for each mol of propylenepresent in the reaction mixture of an acidic sulphuric acid derivativeselected from the group consisting of the aryl sulphonic and chlorosulphonic acids and the lower alkyl esters of sulphuric, aryl sulphonicand chloro sulphonic acids, and. thereafter separating an isopropylester 01' the aliphatic acid from the reaction mixture.

6. In a method of making an isopropyl ester of an aliphatic acid, thesteps which consist of reacting propylene with a substantially anhydrousaliphatic acid under super-atmospheric pressin'e and in the presence ofa catalyst consisting of not more than 0.05 mol for each mol ofpropylene present in the reaction mixture of an acidic sulphuric acidderivative selected from the group consisting of the aryl sulphonic andchloro sulphonic acids and the lower alkyl esters of sulphuric, arylsulphonic and chloro sulphonic acids, fractionally distilling theisopropyi esters of the aliphatic acid from the reaction mixture, andreturning unreacted components of the mixture to the reaction zone.

7. In a method of making an isopropyl ester of an aliphatic acid, thestep which consists in reacting propylene with a substantiallyanhydrousaliphatic acid under super-atmospheric pressure, and in the presence ofa catalyst consisting in a lower alkyl ester of sulphuric acid in amountnot in excess of 0.05 mol for each mol oi propylene present in thereaction mixture.

8. In a method 01 making an isopropyi ester of an aliphatic acidithestep which consists in reacting propylene with a substantially anhydrousaliphatic acid in the presence of a catalyst consisting in di-ethylsulphate inamount not in excess of 0.05 mol for each mol of propylenepresent in the reaction mixture; the reaction mixture being maintainedunder super-atmospheric pressure and at a temperature between about 75C. and about 250 C. during reaction.

GERALD H. COLEMAN.

